This project involves a longitudinal study of the development of nighttime sleep parameters, daytime sleepiness, and performance throughout adolescence. This period of life is emphasized because large differences in 24-hour sleep/wake function have been observed between college-age individuals and pre-adolescent children; pathological sleepiness associated with narcolepsy and Kleine-Levin syndromes characteristically begins in adolescence; and normative data are needed to facilitate early diagnosis and treatment of pathologically sleepy children and adolescents. To date, we have evaluated 25 control children and 11 children with a family history of narcolepsy over five years of study. (Two years were performed without NIH funding). Each child is evaluated for three days every summer. Testing includes overnight recordings of sleep, daily multiple sleep latency testing, and performance testing. Sexual maturation is followed by yearly Tanner staging.